The present invention relates to a new and distinctive corn inbred line, designated KWU7104. There are numerous steps in the development of any novel, desirable plant germplasm. Plant breeding begins with the analysis and definition of problems and weaknesses of the current germplasm, the establishment of program goals, and the definition of specific breeding objectives. The next step is selection of germplasm that possess the traits to meet the program goals.
The goal of plant breeding in corn is to develop inbred parent lines that contribute various desirable traits to the hybrids in which they are used. These traits may include resistance to diseases and insects, tolerance to heat and drought, reducing the time to crop maturity, greater yield, and better agronomic quality. With mechanical harvesting of many crops, uniformity of plant characteristics such as germination and stand establishment, growth rate, stalk strength, root strength, ear retention, maturity and plant and ear height, are important.
Choice of breeding or selection methods depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the type of cultivar used commercially (e.g., F.sub 1 hybrid cultivar, pureline cultivar, etc.) For highly heritable traits, a choice of superior individual plants evaluated at a single location will be effective, whereas for traits with low heritability, selection should be based on mean values obtained from replicated evaluations. Popular selection methods commonly include pedigree selection, modified pedigree selection, mass selection, and recurrent selection.
Field crops can be bred through techniques that take advantage of the plant's method of pollination. A plant is self-pollinated if pollen from one flower is transferred to the same or another flower of the same plant. A plant is cross-pollinated if the pollen comes from a flower on a different plant.
Plants that have been self-pollinated and selected for type for many generations become homozygous at almost all gene loci and produce a uniform population of true breeding progeny. A cross between two homozygous lines produces a uniform population of hybrid plants that may be heterozygous for many gene loci. A cross of two plants each heterozygous at a number of loci will produce a population of hybrid plants that differ genetically and will not be uniform.
Corn plants (Zea mays L.) can be bred by both self-pollination and cross-pollination techniques. Corn has separate male and female flowers on the same plant, located on the tassel and the ear respectively. Natural pollination occurs in corn when the wind blows pollen from the tassels to the silks that protrude from the tops of the incipient ears.
The development of corn hybrids requires the development of homozygous inbred lines, the crossing of these lines, and the evaluation of the crosses. The goal of plant breeding is to develop new, unique and superior corn inbred lines and hybrids. In pedigree selection breeding, the breeder combines the genetic backgrounds of two or more inbred lines or various broad-based sources into breeding pools from which the new inbred lines are developed by selfing and selection of the desired phenotypes. The new inbreds are crossed with other inbred lines and the hybrids from these crosses are thoroughly tested and compared to appropriate standards in environments representative of the commercial target area(s).
Pedigree selection breeding starts with the crossing of two genotypes, each of which may have one or more desirable traits or more desirable characteristics that are lacking in the other or which complement the other. If the two original parents do not provide all of the desired characteristics, other sources can be included in the breeding population. In the pedigree selection method, superior plants are selfed and selected in successive generations. In the succeeding generations, the heterozygous condition gives way to the homozygous lines as a result of self-pollination and selection. Typically in the pedigree method of breeding, five or more generations of selfing and selection are practiced: F1; F2; F3; F4; F5, etc. These selfing generations are sometimes designated as S0, S1, S2, etc with S0 being an equivalent to F1 while S2 is an equivalent to F3, etc.
Descriptions of breeding methods that are commonly used for different traits and crops can be found in one of several reference books (e.g., Allard, R. W. “Principles of Plant Breeding” John Wiley and Son, pp. 115–161, 1960; Simmonds, 1979; Sneep et al., 1979; Fehr, 1987).
A single cross corn hybrid is the cross of two inbred parent lines, each of which has a genotype which compliments the genotype of the other. The hybrid progeny of the first generation is designated F1. In the development of hybrids, only the F1 hybrid plants are sought. Preferred F1 hybrids are more vigorous than their inbred parents. This hybrid vigor, or heterosis, can be manifested in many polygenic traits, including increased vegetative growth and increased yield.
The development of a hybrid corn variety involves three steps: (1) the selection of plants from various germplasm pools; (2) the selfing of the selected plants for several generations to produce a series of inbred lines, which, although different from each other, breed true and are highly uniform; and (3) crossing the selected inbred lines with unrelated inbred lines to produce the hybrid progeny (F1). During the inbreeding process in corn, the vigor of the lines decreases. Vigor is restored when two unrelated inbred lines are crossed to produce the hybrid progeny (F1). An important consequence of the homozygosity and homogeneity of the inbred lines is that the hybrid between any two inbreds will always be the same. Once the inbreds that give a superior hybrid have been identified, the hybrid seed can be produced indefinitely as long as the homogeniety of the inbred parents is maintained.
A single cross hybrid is produced when two inbred lines are crossed to produce the F1 progeny. Much of the hybrid vigor exhibited by F1 hybrids is lost in the next generation (F2). Consequently, seed from hybrid varieties is not used for planting stock.
Corn is an important and valuable field crop. Thus, a continuing goal of plant breeders is to develop consistent performing, high-yielding corn hybrids that are agronomically sound based on stable inbred lines. The reasons for this goal are obvious: to maximize the amount of grain produced with the inputs used and to minimize susceptibility of the crop to environmental stresses. To accomplish this goal, the corn breeder must select and develop superior inbred parental lines for producing hybrids. This requires identification and selection of genetically unique individuals which in a segregating population occur as a result of a combination of crossover events plus the independent assortment of specific combinations of alleles at many gene loci which results in specific genotypes. Based on the number of segregating genes, the frequency of occurrence of an individual with a specific genotype is less than 1 in 10,000. Thus, even if an entire genotype of the parents has been characterized and the desired genotype is know, only a few, if any, individuals having the desired genotype may be found in a large F2 or S1 population. Typically, however, the genotype of neither the parents nor the desired genotype is known in any detail. An agronomically acceptable F1 hybrid will come from a cross between two superior inbred parental lines. There is no assurance that either of these parental lines will produce a superior hybrid when crossed with a different inbred parent line. Thus, the selection or combination of the two parental inbreds provides a unique hybrid that demonstrates characteristics and performance levels that differ from that obtained when either of the parents is crossed with a different inbred parent line.
Once the superior combination of two parental lines is determined by the testing and selection of the F1 hybrid, that F1 hybrid and the performance traits and characteristics of the hybrid can be indefinitely reproduced so long as the parental inbreds are maintained in their homozygosity and the quality and production procedures are accomplished to the purity standards determined by the seed industry regulations.